This disclosure relates to alkylation catalysts and in particular to alkylation catalysts containing magnesium oxide or iron oxide, their methods of preparation and use in alkylation reactions.
Ortho-alkylated hydroxy aromatic compounds are useful for a variety of purposes. For example, ortho-cresol is a useful disinfectant and wood preservative. It is often prepared by the vapor-phase reaction of a phenol with methanol. In another alkylation reaction, ortho-cresol and phenol can both be converted into 2,6-xylenol. This xylenol monomer can be polymerized to form poly(2,6-dimethyl-1,4-phenylene)ether, which is the primary component in certain high-performance thermoplastic products.
Alkylated hydroxy aromatic compounds are usually prepared by the alkylation of the precursor hydroxy aromatic compound with a primary or secondary alcohol. The alkylation must be carried out in the presence of a suitable catalyst, such as a magnesium-based or iron-based compound.
A great deal of attention has been paid to optimizing the performance of magnesium-based catalysts in an industrial setting. Usually, it is very important for the catalyst to have high activity, i.e., it must have as long of an active life as possible. Moreover, the catalyst must have very good ortho-selectivity. Many of the ortho-alkylation catalysts used in the past produced a high proportion of para-alkylated products of marginal utility.
As an illustration, the alkylation of phenol with methanol in the presence of a magnesium oxide catalyst yields ortho-cresol (o-cresol) and 2,6-xylenol, which are desirable products. However, the alkylation reaction may also produce substantial amounts of para-substituted compounds, such as para-cresol (p-cresol), 2,4-xylenol, and mesitol (2,4,6-trimethylphenol). In some end use applications, these para-substituted compounds are much less useful than the corresponding compounds containing unsubstituted para positions.
While improvements in selectivity, activity and catalyst life have been made, there is an ongoing need for improved selectivity, activity and catalyst life in order to improve the efficiency of the alkylation process.